Researchers from the Francis Crick Institute in London, including Dr. George Kassiotis, head of the Laboratory of Retrovirus Immunology and professor of virology in the Department of Medicine at Imperial College, who published the paper in The Lancet medical journal, found that antibodies generated in people who have had only two doses of Oxford/Astra Zeneca or Pfizer/BioNTech are less able to neutralise Omicron than the Alpha and Delta variants. Indicatively, in those who took two doses of Pfizer, antibody levels were found to be about three times lower against Omicron than against Delta after two doses. In those who had taken two doses of Astra Zeneca, anti-Omicron antibody levels were too low to measure.
The scientists, who analyzed 620 blood samples from 364 people, found that antibody levels drop within the first three months after the second dose, but the third dose effectively restores levels so that they no longer neutralize Omicron.
In people who took all three doses with Pfizer/BioNTech, average anti-Omicron antibody levels after the booster dose are similar to those against Delta after two doses. Overall, antibody levels are nearly 2.5 times higher against Omicron after the three doses, compared to the two doses.
Higher anti-Omicron antibody levels were also found in people who took two doses of either Pfizer or Astra Zeneca and also experienced Covid-19 symptoms, compared to those who did not have such symptoms of infection.
Although antibody levels alone do not predict vaccine efficacy, they are a very good indicator of protection against severe Covid-19. The new study confirms that three vaccine doses are necessary to maximise protection against severe disease and the risk of hospitalisation due to Covid-19.
The researchers also confirmed that the synthetic monoclonal antibody Xevudy (sotrovimab), used to prevent and treat patients at risk of becoming seriously ill, can neutralise Omicron.
Source: skai.gr
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